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R J Stockert

Publications and source records attributed to R J Stockert.

At least 73 records · Page 4Linked to original sources
PubMed1982

Asialoglycoprotein receptors in hepatic regeneration.

The hepatic binding protein which is responsible for receptor-mediated endocytosis of desialylated glycoproteins undergoes cell-cycle dependent modulation of its expression. Endocytosis of desialylated orosomucoid by hepatocytes isolated from regenerating liver following two-thirds hepatectomy is reduced by 80% and returns to normal when regeneration is substantially complete. This decrease in endocytotic activity is due to selective loss of cell-surface associated receptor during liver regeneration.

Animals↗
PubMed1982

IgA interaction with the asialoglycoprotein receptor.

IgA present in normal human serum reacts with the hepatic receptor specific for asialoglycoproteins as demonstrated by inhibition of receptor-mediated erythroagglutination. Inhibition is reversibly abolished by the oxidation of the galactose or N-acetylgalactosamine residues of IgA with galactose oxidase. The site of receptor recognition appears to be the O-glycosidically linked oligosaccharides present on the hinge region of the IgAI subtype of IgA. The demonstration of a specific binding, in vitro, of IgA by the hepatic receptor suggests that the uptake of polymeric IgA by the liver in vivo may be mediated by this reaction.

Animals↗
PubMed1982

Effect of nafenopin on the uptake of bilirubin and sulfobromophthalein by isolated perfused rat liver.

Hepatic uptake of bilirubin and sulfobromophthalein has kinetic characteristics suggesting facilitated diffusion. Because these compounds demonstrate mutual competition for uptake, a shared uptake mechanism has been presumed. Previous studies in isolated perfused regenerating liver revealed depressed uptake of bilirubin, sulfobromophthalein, and asialoorosomucoid, a desialylated glycoprotein which enters hepatocytes by receptor-mediated endocytosis. This study was designed to determine whether or not depressed transport seen in liver regeneration occurs in other states of hepatocellular proliferation. Rats were pretreated with nafenopin (200 mg/kg . day x 2), a drug that causes rapid hepatocellular proliferation similar to that seen in regeneration. Twenty-four hours after nafenopin treatment, liver weight increased by 40%. Influx, efflux, and sequestration rate constants in isolated perfused liver were quantitated by a computer fit to the model of Goresky. Results 1 day after nafenopin treatment revealed no change in transport parameters for bilirubin and asialoorosomucoid, but 55% and 49% reductions in influx of sulfobromophthalein and conjugated bilirubin, respectively. These studies suggest that hepatocellular proliferation alone is not responsible for the transport alterations seen during liver regeneration. Nafenopin effectively unmasks differences in uptake of bilirubin and other more water soluble organic anions such as sulfobromophthalein and conjugated bilirubin, suggesting that their uptake mechanisms are partially independent.

Animals↗
PubMed1981

Carbohydrate-specified endocytosis: localization of ligand in the lysosomal compartment.

Carbohydrate-directed endocytosis is mediated by a receptor, the hepatic binding protein; it is responsible for the clearance of galactose-terminated glycoproteins from the circulation. This process was investigated by using lactosaminated ferritin which is recognized by this receptor. Ferritin was seen in elements of an extensive "lysosomal compartment" that includes secretory vacuoles, coated vesicles, and GERL. The compartment marked in hepatocytes by the distribution of ligand is similar to that previously described in Kupffer cells (marked by acid phosphatase reaction product and horseradish peroxidase reaction product).

Animals↗
PubMed1980

Functional segregation of hepatic receptors for asialoglycoproteins during endocytosis.

To examine whether hepatic plasma membrane receptors for asialoglycoproteins are replaced or reutilized during endocytosis, receptors on the surface of isolated hepatocytes were uniquely labeled by neuraminidase treatment. This enzyme abolishes binding of asialo-orosomucoid, a galactose-terminated glycoprotein, and restricts the ligand specificity of the cell surface receptor protein to N-acetylgalactosamine-terminated glycoproteins such as desialylated ovine submaxillary mucin. Although a much larger intracellular pool of apparently identical receptor protein is unaffected by neuraminidase, endocytosis of asialo-orosomucoid does not occur in neuraminidase-treated cells, while endocytosis of desialylated ovine submaxillary mucin is unaffected. Endocytosis of desialylated ovine submaxillary mucin, in amounts far exceeding cell surface binding capacity, is not a consequence of replacement of neuraminidase-treated surface receptor by intracellular receptor. Binding and endocytosis of asialoglycoproteins appear, therefore, to be maintained through a continuous reutilization of plasma membrane receptors rather than through their replacement from an intracellular receptor pool.

Animals↗
PubMed1980

Effects of receptor-specific antibody on the uptake of desialylated glycoproteins in the isolated perfused rat liver.

Removal of the terminal sialic acid residues from most mammalian glycoproteins results in their rapid transfer from the circulation into the liver. In vitro, these desialylated glycoproteins bind to a specific membrane-associated hepatic lectin which has a ubiquitous distribution within the liver cell. In the present study, infusion of a specific antibody to the purified lectin into the portal vein of an isolated perfused rat liver prior to injection of radiolabeled asialoorosomucoid or bilirubin reduced the rate of influx of asialoorosomucoid into the liver by over 80%, while the influx of bilirubin was unchanged. Although uptake of asialoorosomucoid remained blocked for at least 90 min after excess antibody was removed from the perfusion system, the total hepatic content of functional binding protein was nearly normal. These results indicate that interaction with specific cell surface lectin is essential for removal of asialoorosomucoid from the circulation. During the 90 min following infusion of antibody, no functional lectin is restored to the surface of hepatocytes.

Animals↗
PubMed1980

Endocytosis of asialoglycoprotein-enzyme conjugates by hepatocytes.

Desialylated glycoproteins were covalently linked to two cytochemically detectable enzymes, horseradish peroxidase or tyrosinase, and injected intravenously in amounts of approximately 0.5 per cent of total plasma glycoproteins into rats. Comparative studies of the rates of disappearance and distribution of free enzyme and conjugates established that recognition of the conjugates by the plasma membranes of hepatocytes was due to the exposure of the terminal galactose residue of the desialylated glycoproteins. At 1 minute after injection, reaction products of the enzyme markers were seen in coated pits and vesicles, elongated pinocytic channels and pleomorphic vesicles, at or close to the sinusoidal surface of hepatocytes. Vesicles containing reaction products were also observed along the lateral surfaces of hepatocytes. By 10 minutes, reaction products were seen in residual bodies near the biliary poles of hepatocytes. These studies confirm the existence of hepatocellular channels previously seen only with large excess of hemoglobin or following partial hepatectomy. They also indicate that the specific receptor for asialoglycoproteins is not restricted to the sinusoidal surfaces of hepatocytes and that transport to the catabolic sites proceeds via cytoplasmic channels and vesicles.

Animals↗
PubMed1980

Diminished hepatic binding protein for desialylated glycoproteins during chemical hepatocarcinogenesis.

The lectin hepatic binding protein has a specific binding capacity for desialylated serum glycoproteins and is limited to hepatocyte membranes. This binding capacity was reduced by approximately 60% in the neoplastic nodules which resulted from exposure of rat livers to N-2-acetylaminofluorene. The binding capacity of the primary hepatocellular carcinomas which resulted from this regimen was reduced by 95%. The loss of binding capacity was found to be proportional to the decreased concentration of immunologically detectable lectin in the altered tissues.

2-Acetylaminofluorene↗
PubMed1979

Immunocytochemical localization of epoxide hydrase in hyperplastic nodules induced in rat liver by 2-acetylaminofluorene.

A knowledge of the biological characteristics of carcinogen-induced hyperplastic nodules of rat liver may be important in the understanding of cancer development. Although its biological role remains to be elucidated, the level of microsomal epoxide hydrase (epoxide hydrolase, EC 3.3.2.3) is 5- to 7-fold greater in hyperplastic nodules nodules induced by feeding the hepatocarcinogen 2-acetylaminofluorene than in liver of control rats. After removal of the carcinogen from the diet, the high level of the enzyme is maintained in those nodules that persist and in the hepatocellular carcinomas that subsequently develop. The availability of antibody to the epoxide hydrase made it possible to use electron microscopic immunocytochemistry to localize this enzyme in the cells of hyperplastic nodules. The immunocytochemical procedure provides direct visual evidence for the presence of this enzyme in smooth endoplasmic reticulum and also in rough endoplasmic reticulum (including the nuclear envelope) of the nodule's parenchymal cells.

2-Acetylaminofluorene↗
PubMed1977

Hepatic binding protein: the protective role of its sialic acid residues.

Removal of sialic acid from a specific hepatic binding protein virtually abolishes its capacity to bind certain asialoglycoproteins. The loss of this capacity is the result of competition for the binding sites by galactosyl residues, of hepatic binding protein, that become terminal after desialylation.

Acetylgalactosamine↗
PubMed1974

Mammalian hepatic lectin.

A rabbit hepatic protein that specifically binds asialoglycoproteins is also a lectin that agglutinates untreated human and rabbit erythrocytes and neuraminidase-treated erythrocytes from rat, mouse, and guinea pig. Both binding of asialoglycoproteins and agglutination of erythrocytes appear to involve reaction on the same active sites of the hepatic protein.

Agglutination↗
PubMedDate not supplied

Modulation of the transport of bilirubin and asialoorosomucoid during liver regeneration.

The normal rat hepatocyte divides approximately once per year but, following two thirds hepatectomy, rapid cellular replication occurs throughout the remaining liver remnant. Using a multiple indicator dilution technique, single-pass transport of 3H-bilirubin and 125I-asialoorosomucoid was studied in isolated perfused liver from 6 hr to 6 d after two thirds hepatectomy or sham surgery. Influx (k1), efflux (k2), and sequestration (k3) rates were quantitated by computer analysis. k1 for 3H-bilirubin fell by over 50% within 6 hr after two thirds hepatectomy and returned to normal 4 d later. k2 progressively decreased with a nadir at 2 d, and returned to normal by 4 d. k3 was transiently depressed, and became normal within 2 d. Although hepatic uptake of asialoglycoproteins has been thought to be irreversible, the experimental data required k2 and k3 parameters for best fit. Similar to results for 3H-bilirubin, the k1 of 125I-asialoorosomucoid was 20% of normal at 1 d after two thirds hepatectomy, and returned to normal by 6 d. Unlike results for 3H-bilirubin, there was a prolonged 50% reduction of k2 and k3 with return to normal by 6 d. The transport changes during regeneration are independent of reduced liver mass or changes in hepatic spaces of distribution. The fact that influx of both compounds reaches a nadir at the time of greatest cellular proliferation with subsequent return to normal suggests a "maturation" of liver cell function for restoration of these specific hepatocyte functions. Modulation of the hepatocyte receptor for desialylated glycoproteins may also be required for cellular recognition as a prerequisite for proliferative responses.

Animals↗
PubMedDate not supplied

Hepatic lysosomal copper protein in dogs with an inherited copper toxicosis.

Hepatic copper overload inherited as an autosomal recessive trait in Bedlington Terriers is characterized by the presence of hepatocellular lysosomal granules of unusually high specific gravity and electron density which contain at least two thirds of the total hepatic copper. Fractionation of homogenates of liver from such affected Bedlington Terriers yielded a low-speed pellet which contained the lysosomal granules. This fraction was used for isolation of a copper-binding protein by alkaline-reduction, solubilization, fractional acetone precipitation, and gel filtration. The purified protein yielded a single band on polyacrylamide gel electrophoresis and resembled other metallothioneins in containing 15 cysteine residues and 7 to 8 atoms of copper (but no zinc) per 54 amino acid residues. No methionine, histidine, or any aromatic amino acid was present. The accumulation of this lysosomal copper protein appears to be related to the primary genetic defect which underlies the hepatic copper toxicosis of the Bedlington Terrier.

Animals↗
PubMedDate not supplied

Asialoglycoprotein receptor expression in murine pregnancy and development.

Hepatic asialoglycoprotein receptor activity of pregnant mice increased from the tenth day of gestation, reaching 3-fold the normal adult level just prior to parturition and returning to normal within 1 week postpartum. Increases in activity involved both intracellular and cell-surface associated receptors and were associated with enhanced endocytosis of asialoorosomucoid by isolated hepatocytes. Modulation of hepatic binding protein expression during murine pregnancy represents the first situation in which this receptor's concentration has been shown to exceed normal levels in response to a physiologic change. In the fetus, receptor activity was barely detectable throughout gestation, steadily increased in the neonatal period, and reached adult levels by the fifth postpartum day.

Animals↗